Most players are already somewhat familiar with Faction Fight (aka El Antiguo Patrimonio), so this is no big secret. But since there isn't a comprehensive write-up on it, I wrote something for new players and uh, players who are a bit out-of-touch.

Republicans can then enter the Faction Fight Entrances at Thueringen Lakeside (D6), while Royalists can enter at Reboldeaux Queen's Gate (D2). The gates will spawn in Channel 1 only, and will vanish after 30 minutes. Each entry costs 20 Reputation Points. Faction Fight takes place in 2 different maps - one for Royalists, one for Republicans.

About 10 minutes after the gates opened, Ancient Gerero (L112 Daemon) will spawn at the 3 indicated spots in the starting area. When killed, a warp gate will spawn behind Gerero's spawn point.

The warp gate will bring you to another area where Ancient Diablo (L118 Daemon), Ancient Sharffenberger (L120 Human), and Ancient Hell Breaker (L118 Golem) reside. The bosses are accompanied by some minions, like the normal raid versions. When killed, each of them will drop 5 L100 Enchantment Chips and 1 Hero's Seal, and another warp gate will spawn in the middle leading to one of the waiting platforms.

When all three bosses are dead, a warp gate will spawn at both waiting platforms, leading back to the starting area. In the middle of the starting area, there will be a warp gate leading to the last area, where you have to destroy a Royalist/Republican Colony (L136, HP 5000). Some hostile Royalist/Republican Guards (L114-116 Human) may spawn to defend the colony. Once the colony is destroyed, there will be a server-wide notice:

[Notice] Royalists/Republicans have liberated El Antiguo Patrimonio from the Republicans/Royalists.

The colony will be replaced by a Beacon. The faction which destroys the colony first will be able to acquire from the Beacon [Bless of Ancient] buff, which grants the active characters ATK/DEF Rating +1 for 24 hours. The buff persists after becoming mercenary, and is "paused" while the character is in the quarters.

The listed times are for Orpesia server, which is based on PST. Other servers may have different starting times. See also [v2.6 Feature] Arena of the Ancients and 古代の遺跡 for detailed stats of the bosses and other information.

[Sword2] Faction Fight Bug
A bug has existed in Sword 2 for a long time. The event is supposed to be a race against time. The faster faction gets the buff, but the slower faction won't be able to get any buff at all. However, in Sword 2, even the slower faction can still get the buff so long as they managed to destroy the colony. *Shrugs* It doesn't work the way it is supposed to, but since it benefits everyone, I guess nobody bothers to complain about it.

Furthermore, the event requires at least 1 Royalist AND 1 Republican clan to proceed. [Source] If no Royalist (or Republican) show up, then the other side will be stuck. This doesn't seem to be the case in Sword 2 as well.

v5.0 Update
Since v5.0, Ancient Gerero spawned immediately after the main gate is open, instead of 10 minutes later.